The present invention relates to an ultrasonic cutting system for use on foods or other confectionary products. The invention also relates to a method for cutting a material using the ultrasonic cutting system.
The conventional method of ultrasonic cutting involves the use of a cutting blade which is mounted on an ultrasonic vibrating device with the blade lying in a plane containing the longitudinal axis of vibrations, and moving the blade through the article to be cut in said plane. However, difficulty is experienced using such conventional methods in that the depth of the cut that can be attainable is limited.
For this reason, ultrasonic cutting has in general been limited to thin articles such as paper, cloth, and thin plastic sheets. Significant problems exist in cutting blocks of substantial depth, and in providing a number of parallel cuts simultaneously. In the edible confectionery field, the current market trend is towards lighter, softer, and stickier products. Not only are such products difficult to cut ultrasonically, but a lot of waste may result using current cutting techniques. Examples include sticky materials, such as caramel, or composite materials which are composed of different materials having different viscosities or hardness. These confectionery products may include a mixture of chocolate, nougat, caramel, and nuts, which tend to drag causing the product to lift before passing through the cutting blade, or they may bend the cutting blade resulting in a product of uneven width and that is often overheated. Difficulty is also experienced in cutting materials that are brittle or friable, such as honeycomb or crystalline materials, which may shatter if dropped. Often, the cutting blades are not sufficiently reliable for long-term use due to such problems.
In our co-pending application, EP-A-0943405, we describe an ultrasonic cutting system that significantly reduces the above problems and difficulties. The ultrasonic cutting system claimed comprises: an ultrasonic vibrating device having an operative face; a block horn having a responsive face connected to the operative face of the ultrasonic vibrating device and an operative face; and a plurality of cutting blades mounted on the operative face of the block horn, so as to be vibrated therewith. The blades are in a plane containing the longitudinal axis of vibrations, such that the block horn is provided with at least one tuning slot traversing the block horn between the operative and responsive faces.
However, we have found that when using the system described in EP-A-0943405, the fatigue life of the blades is not entirely satisfactory. The ultrasonic system is essentially a resonant structure with enough inherent damping to control the vibrational amplitude. The cut material acts as a damping medium and will stabilize the cutting blades. The main problem is that when the system is removed from the product and runs in the air, the transient force applied to the blades can cause the system to xe2x80x9cmode hopxe2x80x9d , i.e., change from a longitudinal mode of vibration at 36 kHz to a lateral or flexural mode at some lower sub-harmonic. This lateral or flexural mode can be very destructive. The tip amplitude can change from 65 xcexcm up to 2 mm, which causes extreme acceleration forces that can cause the blade to fracture within seconds.
Thus, it is desired to provide an improved ultrasonic system for cutting thicker- and/or stickier-type products while minimizing the tendency of the cutting blade to fracture.
The present invention relates to an ultrasonic cutting system including an ultrasonic vibrating device having an operative face; a block horn having a response face connected to the operative face of the ultrasonic vibrating device, and a second operative face, and being provided with at least one normal tuning slot having a first width traversing the block between its operative and responsive faces and at least one thin tuning and damping slot having a second width traversing the block horn between its operative and responsive faces, wherein the second width is smaller than the first width; and a plurality of cutting blades mounted on the second operative face, so as to be vibrated therewith, the blades lying in a plane containing the longitudinal axis of vibrations.
In a preferred embodiment, the width of the normal tuning slots is from about 4 mm to about 6 mm and the width of the thin tuning slots is from about 0.1 mm to about 2.5 mm. In another embodiment, the length of the block horn between the operative and responsive faces is from about 60 mm to about 70 mm, the width of the operative and responsive faces is from about 60 mm to about 70 mm, and the thickness that the tuning slots traverse is from about 15 mm to about 25 mm. In another embodiment, the block horn includes a shoulder on one or more sides of the responsive face. Preferably, the block horn includes aluminum or titanium.
In another embodiment, the number of cutting blades mounted on the operative face of the block horn is from 2 to 6. In a preferred embodiment, an odd number of cutting blades is used.
In yet another embodiment, the cutting blade is detuned to a value from about 80 Hz to about 200 Hz different from that of the operative face of the block horn, the cutting blade frequency is from about 10 kHz to about 60 kHz, and its amplitude is from about 20 xcexcm to about 250 xcexcm. In another embodiment, the cutting blade is detuned to a value sufficiently different from that of the operative face of the block horn so as to stabilize the system, reduce the gain, and slightly widen the frequency of the operation. The blade is then machined to set its orientation.
In a further embodiment, the blades have a length of about 50 mm to about 100 mm, a thickness of about 1.4 mm to about 3.4 mm, and the distance between them is from about 15 mm to about 35 mm. In another embodiment, the cutting blades are independently offset relative to the vertical axis. In an additional embodiment, the number of normal tuning slots in the blades is one less than the number of cutting blades.
In another embodiment, the thin tuning and damping slots have a width of about 0.15 mm to about 1.0 mm. In another embodiment, a plurality of ultrasonic cutting systems are connected in series to increase the total number of cutting blades. A preferred embodiment has 5 to 10 systems connected in series to provide a total of about 20 to 40 blades.
The invention also relates to an apparatus for cutting a material including: an ultrasonic vibrating device having an operative face; a block horn having a responsive face connected to the operative face of the ultrasonic device and a second operative face, and being provided with at least one normal tuning slot traversing the block horn between its operative and responsive faces having a width of about 4 mm to about 6 mm; a plurality of cutting blades mounted on the operative face of the block horn so as to be vibrated therewith, the blades lying in a plane containing the longitudinal axis of vibrations; means for conveying the material to be cut; and means for causing the cutting blades to ultrasonically vibrate while moving the cutting blades in the plane through the material such that the block horn is also provided with at least one tuning and damping slot having a width of about 0.1 mm to about 2.5 mm traversing the block horn between its operative and responsive faces.
In one embodiment, the material to be cut is conveyed by a conveyor belt which supports the material. Preferably, the material to be cut is conveyed by an upper and lower conveyor belt that reduce lifting of the material as it is conveyed.
The invention further relates to a method for cutting a material, which includes: conveying the material past the ultrasonic system described above; and passing the blades through the material at ultrasonic frequencies so as to cut the material.
In one embodiment, the material is conveyed from beneath the ultrasonic cutting system on a conveyor belt at a speed of up to about 10 meters per minute. In another embodiment, the material to be cut is transported beneath the ultrasonic cutting system between upper and lower conveyor belts to inhibit lifting of the material as it is conveyed. In a further embodiment, the material to be cut is a mixture of two or more of: chocolate, nougat, caramel, nuts, bakery products, snack products, meals, filled dough products, or ice cream. In yet another embodiment, the blades pass through the material at a frequency of about 10 kHz to about 60 kHz.